Monday, December 25, 2006

The Evolution of Language -- IV

I began looking at the issue of the evolution of language because of a philosopher friend's claim that it is somehow obvious that human language is a natural evolutionary development of primate communication systems. As far as I can tell, this is false. What is clearer is that this thesis cannot be proved to be true. There is, in fact, not a shred of evidence for it. There have been cognitive developments by humans not found in other primates and that there have been physiological developments in humans not shared by other primates, both of which help to explain how we might have left them so far behind.

Vocalizations by nonhuman primates in the wild do occur, of course, and we may be sure that they have meaning, perhaps even conventional meaning, but these calls differ in a quite fundamental way from human vocal communication. All human languages employ discrete sounds that do not themselves have either conventional meaning nor meaning in context (meaning as significance) that are combined to form sound sequences (morphemes) that have conventional meaning. The word "ban" is comprised of three sounds, none of which have meaning, but these three sounds when combined to form "ban" do have meaning. Moreover, if we string these three sounds together in another order, as in "nab" we get a word that is entirely different in meaning. No primate vocalizations exhibit this critical property. All human languages do. This compositional property is exhibited at every level of linguistic structure.

The notion that primate communication in the wild can usefully be compared to human communication nevertheless persists. In their paper on social cognition and the origin of language, Seyfarth, Cheney, and Bergman argue that call sequences consisting of individual calls, each of which has a different meaning and which is produced by different animals can combine to form complex messages "that [are] interpreted by listeners in a manner that resembles the way we interpret sentences."1 This claim reminds me of the Huey, Dewey, and Louie sentences of cartoon fame in which each of Donald Duck's nephews contributes words in succession that form whole utterances. The key word in the claim of Seyfarth, Cheney, and Bergman's paper is, of course, the term "resembles." There are few words in the scholarly literature that are weaker than this one. I would be surprised that a paper that is this silly could make it into the scholarly literature if I didn't already know that this sort of thing goes on all the time.

So far observation of nonhuman primates in the wild and such efforts to teach language to them while in captivity as was discussed in prior blogs demonstrates that these animals do not have the capacity to learn human-like languages. The failure derives in part from the absence of the ability to create their own or learn to use signaling devices (ASL signs or computer keyboard chips) we provide. Humans learn languages spontaneously without much help and this includes the learning of oral as well as signed language. I believe that there are two reasons for this inability. Nonhuman primates don't have the cognitive ability to learn human language and, if I may channel Ludwig Wittgenstein for awhile, it seems they don't have much interest in doing so. Wittgenstein claimed that if a Lion could talk, we couldn't understand it. I would argue that nonhuman primates lack the human desire to imitate other humans.

With one avenue to the understanding of how human communication arose closed, we must turn to either the fossil record or to studies of the brains of humans and other animals to search for parallels in animals to the linguistic centers of the human brain such as Broca's area (for speech production and language understanding) and Wernicke's area (for sound processing) and connections between them. As for the fossil record, there is little to say. Language per se leaves no fossil record.

The human vocal tract is capable of producing a wide variety of sounds from such garden variety sounds as the vowel of "bad" to the much more complex clicks of some African languages. One reason we can make so wide a variety of sounds is our "descended larynx." This enlargement of the vocal tract allows humans to modulate sounds issued forth from the larynx. A descended/lowered larynx was once believed to be unique to humans and an evolutionary adaptation for language but it seems that there are other animals that have a descended larynx which do not have language. Fitch and Reby claim that there are deer that exhibit this property. They make the point that since deer do not have anything like human speech, we would not want to infer a capacity for human like speech for any species based on fossils exhibiting a descended larynx. They point out that deer exaggerate their body size by further enlarging the length of their vocal tracts which results in sounds of a lower frequency. In general, the lower the frequency of an animal's vocalizations, the larger it is. A need to seem bigger and stronger to survive may be why we developed a lowered larynx, but their are other theories.

One of the interesting ironies of research on nonhuman primate oral productions in the wild and of the teaching of human language to nonhuman primates is that various animal species can imitate human speech such as birds (parrots) and even seals it seems, but nonhuman primates cannot do so. The ability to imitate speech is, of course, of huge importance to language learning for without that capacity children could not learn language. As I noted above, we humans have a strong, innate desire to imitate other humans. Nonhuman primates do not have a desire to imitate us. That is part of the problem of teaching them language. They don't want to be humans. They want to be monkeys or bonobos or gorillas.

Fitch and Reby in the two papers referenced note that a great number of adaptations would have had to be acquired for language as we know it to have evolved. We required not just a descended larynx but a very talented tongue, and quite talented lips, as well as the motor control to coordinate the various physiological events required to create human sounds. In addition, our sound perception abilities had to emerge to allow us to discriminate linguistic sounds from others. This ability to discriminate speech sounds from others occurs very early in life, but as infants become familiar with the sounds of a particular language they, like adults, become less facile perceptually. See Maye, Werker, and Gerken's paper if you can get access to it.

The development of our talented vocal tracts and the motor skills to employ it and the development of our perceptual abilities have purely physiological sides but also required significant cognitive development. Of course, the ability to hear and the ability to discriminate sounds by animals of the same species is hardly restricted to humans. Essentially all hearing animals have that ability and we would expect such animals to develop homologues to our Wernicke's area for sound perception and to our Broca's area for sound production. There is no evidence that these areas are as richly developed in other animals as they are in humans.

What we may be quite sure of is that the different physiological developments required for the production and understanding of speech, did not occur simultaneously. Rather, they must have evolved over a long period of time. Moreover, the purely cognitive side of language will not have developed full blown over night but incrementally and we can imagine that as our vocal abilities increased our computational linguistic-cum-cognitive abilities will have increased as well. From a linguistic point of view, the problem of understanding of the evolution of language is not that there is a "missing link" but that there are a multiplicity of them. So, the claim with which we began -- that the evolution of human language is somehow linked to the evolution of animal modes of communication is false, in my view, but is clearly unprovable. There is no evidence supporting this view whatever beyond the fact that animals, like humans, can communicate. And that doesn't make what they do linguistic.1Robert M. Seyfarth, Dorothy L. Cheney and Thore J. Bergman, "Primate social cognition and the origins of language" in Trends in Cognitive Sciences Vol.9 No.6 June 2005.